Cadmium and lead thiophosphate additives for lubricating oil compositions



United States Patent 3,232,873 CADMIUM AND LEAD THIOPHOSPHATE ADDI- TIVES FOR LUBRICATING OIL CQMPOSITIONS Ernest V. Wilson, Cranford, Henry R. Ertelt and Jack Rockett, Westfield, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Apr. 23, 1963, Ser. No. 274,951 2 Claims. (Cl. 252--32.7)

This invention relates to an improved lubricating oil additive, and to lubricating oil compositions containing said additive which have low neutralization numbers and high-load carrying properties. More particularly this invention relates to cadmium di(secondary)alkyl dithiophosphates and to lubricating oil compositions comprising a major proportion of a lubricating oil and minor amounts of these cadmium dithiophosphates.

This application is a continuation-in-part of our Serial No. 850,462, filed November 2, 1959, and now abandoned.

The use of metal thiophosphates to improve the loadcarrying ability of mineral lubricating oils has been disclosed in the prior art. Zinc thiophosphates have been used almost exclusively, however, for this purpose. The use of zinc thiophosphates has not been entirely acceptable since this type of metal thiophosphate imparts an unsatisfactorily high acidity (high neutralization number) to the oil. It is well recognized in the prior art that a good lubricating oil composition and particularly turbine oi-ls should be nearly neutral, that is, the lubricating oil composition should have an extremely low neutralization number. Lubricating oil compositions that are slightly acidic are frowned upon because they often induce corrosion, while lubricating oil compositions which are excessively basic often tend to create sludging problems both in storage and in use. While the titratable acidity of zinc dialkyl dithiophosphate (ZDDP) is not normally corrosive, it does interfere with tests made on the oil in service. For example, it is a well established practice to take neutralization number measurements on turbine oils at regular intervals to determine the condition of the lubricant. When the neutralization number gets above a certain level (owing to the formation of oxidation products) the user knows that the oil is becoming unstable and replaces it before damage to equipment can occur. The interference of ZDDP with this well-established practice is a serious barrier to commercial acceptance and naval approval of ZDDP-containing turbine oils. In view of these problems, most purchasers of lubricants of the type used in lubricating turbines require a maximum neutralization number below 0.2 in ther specifications. now been found that replacing ZDDP with cadmium dialkyl dithiophosphates gives a finished oil of a suitably low neutralization number.

The improved lubricating oil compositions of this invention have a maximum neutralization number (ASTM D974) below 0.2 and an extremely high load-carrying ability. It has been found, and this finding terms the basis of the present invention, that in order to form this type of lubricating oil composition, the thiophosphates must be dialkyl dithiophosphates derived from secondary alcohols. In order to give a sufliciently oil soluble dialkyl dithiophosphate, these secondary alcohols will generally average at least about 4.5 carbon atoms per alkyl group and preferably 6 to 12 carbon atoms per alkyl group.

It has i Secondary alcohols having from 3 to about 20, erg. 13-13 carbon atoms may be used. It is also essential that the metal of the metal dithiophosphate be cadmium. Lubricating oil compositions containing up to about 3.0 weight percent of this type of dithiophosphate (with C average alkyl groups) will have an ASTM D974 neutralization number below 0.2. Lubricating oil compositions containing above about 0.75 Wt. percent of this type of thiophosphate will carry in excess of 3,000 lbs./ inch in the Ryder gear test described in the Wright Air Development Center, Detailed Handbook on Test Procedures in Support of Turbojet and Turboprop Lubes, also Military Specification }/III1L17331A (SHIPS), 4.6.2. Lower concentrations of the dithiophosphates of this invention may be used when the requirements for load carrying are not so severe. Thus, the lubricating oil compositions of this in vention will contain from about 0.20 to about 3.0 Wt. percent, e.g. 0.375 to 1.5 wt. percent of the cadmium dialkyl dithiophosphate of this invention. I

The metal dialkyl dithiophosphates of this invention will have the following general formula:

wherein R and R represent secondary alkyl groups each having from 3 to about 20 carbon atoms. The average of R and R will be at least about 4.5 carbon atoms. Preferably R and R will average in the range of about 6 to about 12 carbon atoms. M represents the cadmium.

The lubricating oil can be any conventional oil of lubricating grade known to the art including animal, vegetable, synthetic and mineral oils, the latter being preferred. Preferably the oil base has a viscosity in the range of 37 to 150 Saybolt seconds Universal at 210 F., a viscosity index in the range of 50 to 150, a flash point above 370 F., a pour point below 25 F. and a gravity in the range of 26 to 34 APl. For turbine oil use a solvent neutral type of oil having a viscosity index in the range of to is generally preferred.

Lubricating oil compositions of this invention will also normally contain 0.005 to 0.5; e.g. 0.01 to 0.l0 weight percent of a corrosion inhibitor. As is well known in the prior art (a variety of corrosion inhibitors may be used in lubricating oils according to the type of service contemplated. For the critical turbineoils that are the preferred compositions of this invention, corrosion inhibitors which have been found to be extremely useful include mercaptoacetic acids having the following formula: R SCH COOH wherein R is a branched alkyl group containing in the range of 9 to17 carbon atoms. Preferably R is a branched aklyl group of about 13 carbon atoms.

Also useful as rust inhibitors in the compositions of this invention are the alkenyl succinic acids having the following general formula:

wherein R represents an unsaturated aliphatic radical having about 10 to 22 preferably about 12 to 18 carbon atoms. Compounds wherein R is saturated are similarly useful. Rust inhibitors of this type are well known to the art and are described in U.S. Patents, e.g. 2,124,628

and 2,133,734. In practice the R group is generally a mixture of varying chain length averaging about C to C Such compositions are preferred rust inhibitors for use in the lubricating oil compositions of this invention. The succinic acid or mercaptoacetic acid type rust inhibitors will be used in concentrations in the range of 0.01 to 0.10 weight percent based on the total weight of the lubricating composition. Preferably, the concentrations of succinic acid type rust inhibitor will be in the range of 0.03 to 0.05 weight percent of the total composition. Other rust inhibitors which may be used include dinonyl naphthalene sulfonates as described in U.S. Patent 2,764,548.

For most applications the oxidation stability and loadcarrying ability imparted to the lubricating oil by the dithiophosphate additives of this invention will be entirely adequate. In some specialized applications it may be desirable to include supplemental additives. Supplemental oxidation inhibitors include the phenolic and amine inhibitors Well known in the art, e.g. 2,6-di t-butyl-p-cresol or phenyl u-naphthylamine. Additional extreme pressure additives which may be used include halogen-containing organic compounds such as chlorinated hydrocarbons, e.g. chlorinated wax and chlorinated terpenes such as chlorinated camphene. Such extreme pressure agents are well known in the art. The chlorinated hydrocarbons are particularly useful in certain low speed applications and may be used in concentrations inthe range of from about 0.20 to about 5 weight percent of the total lubricant composition. When such Supplemental additives are used within the concept of this invention they will be added to an oil formulation which by virtue of the lead or cadmium dialkyl dithiophosphate alone will have a low neutralization number, an improved load-carrying ability, and good oxidation stability, e.g. an oil passing the MIL-17331A (SHIPS), September 27, 1955, requirements for these three properties.

The dialkyl dithiophosphoric acid salts of this invention are normally prepared by reacting the secondary alcohol or alcohol mixture containing a secondary alcohol with phosphorus pentasulfide and then forming the cadmium salt by direct neutralization with cadmium oxide Alternatively they may be prepared by double decomposition, e.g. by the reaction of an aqueous solution of an inorganic cadmium salt with an alkali metal dialkyl dithiophosphate to form the corresponding cadmium dialkyl dithiophosphate. Regardless of the route of preparation, it is desired that the product have a low neutralization number and a composition corresponding closely to the theoretical values. The cadmium salt preparation is normally prepared by direct neutralization of the acid with cadmium oxide (although good additives have been prepared by double decomposition). The acid preparation involves the reaction of stoichiometric amounts of alcohol and phosphorus pentasulfide at a temperature in the range of 160 to 200 F., e.g. 185 to 190 F, for about 1 to 6 hrs., e.g. about 3 hrs. The acid will generally be filtered. The neutralization of the acid with CdO will be carried out at a temperature in the range of about 80 to about 200 R, eg. 120 to 170 F. and will continue until the product is essentially neutral, about 1 to 6 hrs., e.g. about 3 t0 4 h It is understood that he empe atures and p r ularly the time of reaction will vary according to the size of the reaction mixture, the equipment being used, etc. The product will usually be diluted with mineral oil or other suitable solvent to form a concentrate more easily handled than the pure additive. While satisfactory products have been prepared under a variety of conditions within the ranges set forth above, for most consistent production of a satisfactory additive certain additional steps are taken. These are: (1) the phosphorus content of the P 8 is kept under the theoretical value of 27.87 wt. percent, preferably below about 27.8 e.g. 26.0-27.5; (2) the acid is blown free of H S with an inert gas, e.g. nitrogen, before neutralization, (3) elemental sulfur is added to the acid immediately before the neutralization. The last item, (3) above is not always necessary if the P 8 used in the acid preparation has a phosphorus content toward the lower end of the range given in step (1) above. Of these precautionary steps, (1) appears most important.

In practice, the P/ S ratio in commercial P 5 may vary somewhat without having any immediately obvious effect on the appearance of reactivity of the dialkyl dithiophosphate product. Commercial P S generally has a phosphorus content above theoretical, e.g., 28.0-28.5 wt. percent P, probably because the high P product is preferred in the manufacture of insecticides. Thus conventional high phosphorus P 8 is definitely not preferred in the manufacture of the additives of this invention. This point is illustrated in a later example.

The lubricating oil compositions of this invention are prepared by simple blending of the cadmium dithiophosphate in concentrations in the range of .20 to 3.0, e.g., 0.375 to 1.5 weight percent dithiophosphate based on the total Weight of the lubricating oil composition. The dithiophosphates may be used without diluent or as an oil solution containing for example, about 50 to dithiophosphate. Other additives which may be added to the lubricating oil compositions of this invention include viscosity index improvers, pour point depressants, extreme pressure agents, antioxidants and antifoamants. Ordinarily detergent additives are not added to the turbine oil compositions which are the particularly preferred embodiment of this invention. However, it is within the scope of this invention that the particular cadmium thiophosphates herein described may advantageously be used in lubricating compositions containing detergent additives.

Antifoamants are normally not required in the lubricating oil compositions of this invention. However, a silicone fluid may be used as an antifoamant if desired. The silicone fluid, if used, will be used in concentrations ranging from 0.0001 to about 0.01 weight percent based on the total weight of the composition. Of particular utility for obtaining additional antifoaming properties in the lubricants of this invention is Dow Corning Fluid 200'.

In summary, this invention relates to a new and improved additive comprising the oil soluble metal salt of a dialkyl dithiophosphoric acid having at least about 9 carbon atoms wherein the metal is cadmium and the alkyl groups are derived from secondary alcohols having from 3 to about 20, e.g., 3 to 13, carbon atoms each. The invention also relates to lubricating oil compositions comprising a major proportion of a lubricating oil and up to 3.0 wt. percent, e.g., 0.375 to 1.5 wt. percent, based on the total weight of the lubricant, of the improved additive. Lubricating oil compositions containing this type of cadmium dialkyl dithiophosphate will have an extremely high load carrying ability, good oxidation resistance, and a low neutralization number. The combination of high load carrying ability with low neutralization number is required. in most turbine oil military specifications such as those: of the United States, British and Canadian Naval specifications. Thus, in a particularly preferred embodiment of' this invention, the lubricating composition will have an ASTM 13-974 neutralization number below about 0.2.

EXAMPLE I The following table illustrates the preparation of the cadmium dialkyl dithiophosphates of this invention (Sainples 1, 2, 3, and 4). In addition the table also discloses the preparation of a similar cadmium dialkyl dithiophosphate that has been prepared from an acid having primary alkyl groups (Sample A comparison of the pH and neutralization number (ASTM D-974, i.e., milligrams of KOH per gram additive) of the products of Samples 1-4 with Sample 5 illustrates that the preferred process of this invention gives a more neutral cadimum dialkyl dithiophosphate additive. While the table shows substantial differences in neutralization number according to the method of preparation, it should be borne in mind that all of the cadmium compounds in the table have far lower neutralization numbers than have the corresponding zinc compounds regardless of the details of preparation. A typical ZDDP di-c -dithiophosphate corresponding to Samples 2, 3, and 5 had a neutralization number of 171.8 and a pH of 5.4 as a 75 wt. percent solution of additive in refined coastal distillate having a nominal viscosity at 210 F. of 40 SSU.

TABLE II.EFFECT or PHOSPHORUS CONTENT OF Pass [Acid prod.: Methyl isobutyl carbinol plus Pass for 3 hours at 190 F., acid cooled and filtered] Run Acid Sulfur, wt. percen Phosphorus, wt. porcent. Ratio, S/P 1 Neutralization:

OdO, percent theory.. 110 110 110 140 120 120 Reaction time, hrs 3 3 3 5 4 4 Reaction temp,

max. F 210 210 187 204 170 170 Product: 2

Sulfur, wt. percent- 12. 43 12. 79 13. 39 18. 7 13.1 13. 7 Phosphorus, wt.

percent 6. 77 6. 74 6. 6. 5 6. 5 6. 5 Cadmium, wt.

percent 9. 10. 30 11.80 11.7 11.8 11.8 Neut. No. 13-974. 35. 5 23. 9 6. 78 5. 58 2. 87 5. 73 Ratio, 8/]? 1 l. 84 1. 90 2. 11 2. 11 2. O2 2. 11 Ratio, Od/P 3 1.43 1. 53 1. 86 1.80 1.82 1. 82

1 Theoretical is 2.07.

2 75 wt. percent Cadmium DDP in refined coastal distillate having a nominal viscosity at 210 F. of ESSU.

Theoretical is 1.81.

4 Not blown Hes free with N2.

5 Blown H2S free with N2.

TABLE I.-PREPARATION OF CADMIUM DIALKYL DITHIOPHOSIHATES Samples Acid preparation Alcohol 0 /0 M1130 M1180 "MIBC O /C P 8 percent theory 10 100 10 100 100 Reaction time, hrs 3 3 3 3 3 Reaction temp, 185 185 185 185 165 Sp. gravity, F-.. 1. 048 0.996 0. 996 0. 990 Neut. N0., D974 206 176 167 217 Phosphorus, wt. percent 11.76 10. 06 9. 90 9. 12.00 Sulfunwt. percent--. 23. 67 20. 69 20. 38 19. 7 25. 04 Ratio, S/P 2.02 2.06 2.06 2. 04 2.09 Neutralization CdO, percent theory 140 140 140 130 1 Reaction time, hrs. 9 4 7 3 3 Reaction temp, I 185 185 185 185 185 Final pH 7. 8 7.8 8.0 2. 7 5. 5 Products:*

Cadmium, wt. percent. 13. 29 11.74 11. 64 10. 91 9. 22

Phosphorus, wt. percent 7. 37 6.16 6. 44 6. 58 10. 16

Sulfur, Wt. percent. 15. 88 13. 81 13. 57 13. 30 20. 60

Ratio, Cd/P 3 1.80 1. 90 1.80 1. 66 0.91

Ratio, SIP 2 2. 16 2. 24 2. 10 2.02 2.03

N eut. No. D-974 6. 0 3.3 3. 2 7. 8 13. 6

5 Alcohol mixture 625/375 weight ratio secondary butanol/meghyl isobutyl carbinol.

6 0.5 wt. percent flowers of sulfur (based on acid) added to ac 1 Methyl isobutyl carbinol.

8 Alcohol mixture 65/35 weight ratio isobutyl (primary) lmixed amyl alcohol (primary). *As 75 wt. percent solutions of additive in refined coastal distillate having a nominal viscosity at 210 F. of 40 SSU.

The elfect of P S phosphorus content on the composition of dialkyl dithiophosph-ates is shown in Table II. In particular, this table shows that the high phosphorus P 5 gave dialkyl dithiophosphoric acid with the proper apparent composition as shown by the S/ P ratio, but led to neutralized products having compositions quite far from B. Preparation and properties of. lubricating oil compositions the theoretical values. By comparison, preparations using 70 phosphate (17) the cadmium (ii-C6 (Secondary) and (C) P 5 with less than the 27.87 theoretical weight percent phosphorus content gave products corresponding closely to theory under a variety of conditions. The neutralization numbers of the products prepared from the lower phosphorus P 8 were also markedly lower.

the comparzitive di-C /C (primary) dithiophosphate of Table I. The composition of the lubricants and their neutralization numbers are given in Table III. The dithiophosphate additives of lubricants (b) and (c) correspond to additive Samples 5 and 2 respectively.

FORMULATIONS Mineral oil, 60 SSU vis at 210 F., VI 105 containing:

0.35 wt. percent zinc di- 0.563 wt. percent Cadmi- 0.563 wt. percent cadmium /0 0) ditliiopliosuni di-C /C primary di-C dithiopliosphate, phate, 0.03 wt. percent ditliiophospliate, 0.05 0.03 wt. percent 0 0x0 C oxo mercaptoacetic wt. percent 0 0x0 mermercaptoacetic acid, acid, 0.005 wt. percent captoacetic acid, 0.0005 0.005 wt. percent polypolydiinethylsiloxa-ne wt. percent polydidimethylsiloxane metliylsiloxane 3 Neutralization No., ASTM D-974 0.81 0.32 0.11 OEP oxidation test: Neut. N 0. after oxidation B 0. 32 0. 12

I 11.8. and Canadian Navy specification limit is 0.2 max. neut. number. 2 British Navy (Admiralty DEF-90) specification limit is 0.2 max. neut. number after oxidation.

3 Dow Corning DC-200 silicone fluid.

4 70 wt. percent methyl isobutyl carbinol (secondary) and 30 wt. percent isopropyl (secondary) alcohol.

The above table clearly shows that only those lubri- TABLE Eg B g DATA ON LUBRI- cants formulated from the dithiophosphates of this invention (i.e. cadmium compounds derived [from secondary A B OEILQO alcohols) meet the low neutralization number requirerequirement merits of the U.S., Canadian and British Navies as regards marine tunb-ine lubricating oil formulations. Flash point (closed), F 380 385 330 min.

To further illustrate the improved properties of the vlscoslgy 00s 9 v th f n 100 82.62 8.01 s2to92. u meet ing or composi ion 0 is lll VCIl 1011 e 0 owing 9472 82 mm formulations were prepared With the cadmium dithio- 105 25 15 20 max. phosphates, of this invention. Table IV gives the Weight N11 N11 percent composition of the lubricant formulations. I No 1 1 No lot N 1 N I N l t o. 0.1 o irni TABLE IV.LUBRICANT COMPOSITION Slight Slight. N0 rusty Oxidation stability; Neut. 0.04; 0.03 0.01; 0.02 0.20 max. tion Lubri- Wt. percent Cd Wt. percent 013 Wt. percent alkenyl f 150 195 300 m cant 1 iii-C dithiooxo mercaptcsuccinic acid 3 S1 mun phosphate 2 acetic acid 40 IAE b 103d 98 112 1 0O 0 03 *Canadian Navy Specification is also 90. The OEP-90 re uirements of Table VI are the marine 1.25 0. 03 q 1.50 0.035 turbine 011 specification requirements imposed by the British Admiralty. 33%50 (fiil is a Xr nlinefiraioil of hgigligoritgiseznt ()(Iiigil hgvinfiggg vis lc gsitly at Tables V and VI clearly illustrate the high load-carrying 210 .o60,a 01.8,ai1 0 .an a as o eiasc oil also contained 0.0005 wt. percent of dimethyl silicone fluid (Dow Propgrtles neutrahzatlon P lubn' Corning D0400). I t cants of this invention, as Well as, their oxidation resistance fiffiif g fig of Samples 2 and 3 of Table pace and corrosion inhibiting properties. A comparison of the 3A1keny1grm1p averaging about 16 to 18 carbon s. 50 Sea Water Rust Tests of Tables V and VI indicate that The lubricants at Table IV were then tested as shown in Tables V and VI.

TABLE V.-LUBRICANT QUALITY the alkenyl succinic acid type rust inhibitors impart somewhat better rust inhibition to the lubricating oil composition;

U.S. Navy MIL-L- A B C D 17331A requirements ASTM D-943 oxidation life, hrs 2,000+. 2,000+ 2,000+ 2,000+. 1,000 min. Neutralization N0., ASIM 13-974... 0.12 0.13 0.16 0.12 0.20 max. Copper strip corrosion:

3 hrs. at 212 F Pass.. Pass Pass Pass Slight tarnish or discoloration.

3 hrs. at 250 F do Permitted. Emulsion test at F. 0(15). 0(15) 3(15) 3 ml. lacy (30 min.)

max. Steam emulsion 4 131-.. 139...- 149 99 Sea water rust 5 3 specks Trace N0 rust.-. N0 rust... No rust.

rus Ryder gear load, lbs/in. (average) 3,490 4,560 3,910 3,690 2,200.

Test discontinued afiter more than 2,000 hrs.

VVL791, Method N0. 3201.5 1111. emulsion (time in minutes). 4 AS'IM D-157-51T.

5 ASTM D-665.

Wright Air Development Center, Detailed Handbook on Test Procedures in Support Turbojet and Turboprop Lubes.

This invention, therefore, presents a unique class of dialkyl dithiophosphates having a low neutralization number and capable of imparting to lubricating compositions excellent load-carrying ability (as well as oxidation stability) without raising the neutralization number of the lubricant above the low level required in many commercial applications.

What is claimed is:

1. A turbine lubricating oil composition having improved load-carrying ability and an ASTM D974 neutralization number below 0.2 comprising a major proportion of mineral lubricating oil and about 0.2 to 3.0 wt. percent, based on the total weight of the composition of cadmium dialkyl dithiophosphate, wherein said alkyl groups and alkyl groups of C to C secondary alcohol, said dithiophosphate having a total of at least 9. carbon atoms and being prepared by reacting said secondary alcohol with P 8 having a phosphorus content of about 26 to 27.8 wt. percent to form dithiophosphoric acid, followed by neutralization of said dithiophosphoric acid with cadmium base to thereby form said dithiophosphate.

2. A turbine oil according to claim 1, wherein said secondary alcohol contains 4 to 6 carbon atoms, and wherein said dithiophosphoric acid is blown free of H 8 with nitrogen before neutralizing with said cadmium base, and wherein said cadmium base is cadmium oxide.

References Cited by the Examiner UNITED STATES PATENTS 2,739,123 3/1956 Kennerly et al 25232.7 2,773,860 12/1956 Musselman 252-327 2,932,614 4/1960 Lynch et al. 25232.7

DANIEL E. WYMAN, Primary Examiner. 

1. A TURBINE LUBRICATING OIL COMPOSITION HAVING IMPROVED LOAD-CARRYING ABILITY AND AN ASTM D-974 NEUTRALIZATION NUMBER BELOW 0.2 COMPRISING A MAJOR PROPORTION OF MINERAL LUBRICATING OIL AND ABOUT 0.2 TO 3.0 WT. PERCENT, BASED ON THE TOTAL WEIGHT OF THE COMPOSITION OF CADMIUM DIALKYL DITHIOPHOSPHATE, WHEREIN SAID ALKYL GROUPS AND ALKYL GROUPS OF C3 TO C13 SECONDARY ALCOHOL, SAID DITHIOPHOSPHATE HAVING A TOTAL OF AT LEAST 9 CARBON ATOMS AND BEING PREPARED BY REACTING SAID SECONDARY ALCOHOL WITH P2S5 HAVING A PHOSPHORUS CONTENT OF ABOUT 26 TO 27.8 WT. PERCENT TO FORM DITHIOPHOSPHORIC ACID, FOLLOWED BY NEUTRALIZATION OF SAID DITHIOPHOSPHORIC ACID WITH CADMIUM BASE TO THEREBY FORM SAID DITHIOPHOSPHATE. 